Method and device for packaging a substrate

ABSTRACT

A package structure and method of packaging for an interferometric modulator. A thin film material is deposited over an interferometric modulator and transparent substrate to encapsulate the interferometric modulator. A gap or cavity between the interferometric modulator and the thin film provides a space in which mechanical parts of the interferometric modulator may move. The gap is created by removal of a sacrificial layer that is deposited over the interferometric modulator.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.11/045,738, filed Jan. 28, 2005, which claims priority to U.S.Provisional Application No. 60/613,318, filed Sep. 27, 2004, thecontents of each of which are hereby incorporated by reference in theirentirety.

BACKGROUND

1. Field of the Invention

The field of the invention relates to microelectromechanical systems(MEMS) and the packaging of such systems. More specifically, the fieldof the Invention relates to interferometric modulators and methods offabricating such modulators with thin film backplanes.

2. Description of the Related Technology

Microelectromechanical systems (MEMS) include micro mechanical elements,actuators, and electronics. Micromechanical elements may be createdusing deposition, etching, and or other micromachining processes thatetch away parts of substrates and/or deposited material layers or thatadd layers to form electrical and electromechanical devices. One type ofMEMS device is called an interferometric modulator. An interferometricmodulator may comprise a pair of conductive plates, one or both of whichmay be transparent and/or reflective in whole or part and capable ofrelative motion upon application of an appropriate electrical signal.One plate may comprise a stationary layer deposited on a substrate, theother plate may comprise a metallic membrane separated from thestationary layer by an air gap. Such devices have a wide range ofapplications, and it would be beneficial in the art to utilize and/ormodify the characteristics of these types of devices so that theirfeatures can be exploited in improving existing products and creatingnew products that have not yet been developed.

SUMMARY OF THE INVENTION

The system, method, and devices of the invention each have severalaspects, no single one of which is solely responsible for its desirableattributes. Without limiting the scope of this invention, its moreprominent features will now be discussed briefly. After considering thisdiscussion, and particularly after reading the section entitled“Detailed Description of Certain Embodiments” one will understand howthe features of this invention provide advantages over other displaydevices.

An embodiment provides a package structure for an interferometricmodulator display device that eliminates the need for a separatebackplane, desiccant, and seal. The display device includes atransparent substrate, an interferometric modulator configured tomodulate light transmitted through the transparent substrate, and a thinfilm backplane disposed on the modulator and sealing the modulatorwithin a package between the transparent substrate and the thin filmbackplane. A gap exists between the modulator and the thin film and iscreated by the removal of a sacrificial layer.

In accordance with another embodiment, a method of manufacturing adisplay device is provided. According to this method, a transparentsubstrate is provided and an interferometric modulator is formed on thetransparent substrate. A thin film backplane is then deposited over theinterferometric modulator and the transparent substrate to seal themodulator between the transparent substrate and the thin film backplane.A sacrificial layer is deposited on the interferometric modulator priorto deposition of the thin film backplane. The sacrificial layer isremoved after deposition of the thin film backplane to create a gapbetween said interferometric modulator and the thin film backplane.

In accordance with yet another embodiment, a microelectromechanicalsystems display device is provided, comprising a transparent substrate,an interferometric modulator formed on the transparent substrate, and athin film backplane sealed to the transparent substrate to encapsulatethe interferometric modulator between the transparent substrate and thethin film backplane. A cavity exists between the interferometricmodulator and the thin film backplane. The cavity is created by removinga sacrificial layer between the interferometric modulator and the thinfilm backplane.

According to another embodiment, a display device is provided,comprising a transparent substrate, an interferometric modulator, a thinfilm backplane deposited over the interferometric modulator, and acavity between the modulator and the thin film backplane. Theinterferometric modulator is configured to modulate light transmittedthrough the transparent substrate, and is formed on the transparentsubstrate. The thin film backplane is deposited over the interferometricmodulator to seal the modulator within a package between the transparentsubstrate and the thin film backplane. The cavity is formed by removinga sacrificial material.

According to yet another embodiment, a display device is provided. Thedisplay device includes a transmitting means for transmitting lighttherethrough, a modulating means configured to modulating lighttransmitted through the transmitting means, and a sealing means forsealing the modulating means within a package between the transmittingmeans and the sealing means. The modulating means comprises aninterferometric modulator, and the sealing means comprises a thin film.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the invention will be readily apparent fromthe following description and from the appended drawings (not to scale),which are meant to illustrate and not to limit the invention, andwherein:

FIG. 1 is an isometric view depicting a portion of one embodiment of aninterferometric modulator display in which a movable reflective layer ofa first interferometric modulator is in a released position and amovable reflective layer of a second interferometric modulator is in anactuated position.

FIG. 2 is a system block diagram illustrating one embodiment of anelectronic device incorporating a 3×3 interferometric modulator display.

FIG. 3 is a diagram of movable mirror position versus applied voltagefor one exemplary embodiment of an interferometric modulator of FIG. 1.

FIG. 4 is an illustration of a set of row and column voltages that maybe used to drive an interferometric modulator display.

FIGS. 5A and 5B illustrate one exemplary timing diagram for row andcolumn signals that may be used to write a frame of display data to the3×3 interferometric modulator display of FIG. 2.

FIG. 6A is a cross section of the device of FIG. 1.

FIG. 6B is a cross section of an alternative embodiment of aninterferometric modulator.

FIG. 6C is a cross section of another alternative embodiment of aninterferometric modulator.

FIG. 7 schematically illustrates a package structure in which aninterferometric modulator is packaged without a conventional backplane,according to an embodiment.

FIG. 8 is a flow chart of an embodiment of a method to packageinterferometric modulators.

FIG. 9 schematically illustrates a package structure in which asacrificial layer has been deposited over the interferometric modulator,according to an embodiment.

FIG. 10 schematically illustrates a package structure in a thin film hasbeen deposited over the sacrificial layer.

FIG. 11 is a top view of an embodiment of the package structure 800after the thin film 820 has been deposited and patterned and before thesacrificial layer 850 is released.

FIG. 12 schematically illustrates a package structure in which aninterferometric modulator is packaged according to an embodiment andhaving an overcoat layer.

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS

The following detailed description is directed to certain specificembodiments of the invention. However, the invention can be embodied ina multitude of different ways. In this description, reference is made tothe drawings wherein like parts are designated with like numeralsthroughout. As will be apparent from the following description, theinvention may be implemented in any device that is configured to displayan image, whether in motion (e.g., video) or stationary (e.g., stillimage), and whether textual or pictorial. More particularly, it iscontemplated that the invention may be implemented in or associated witha variety of electronic devices such as, but not limited to, mobiletelephones, wireless devices, personal data assistants (PDAs), hand-heldor portable computers, GPS receivers/navigators, cameras, MP3 players,camcorders, game consoles, wrist watches, clocks, calculators,television monitors, flat panel displays, computer monitors, autodisplays (e.g., odometer display, etc.), cockpit controls and/ordisplays, display of camera views (e.g., display of a rear view camerain a vehicle), electronic photographs, electronic billboards or signs,projectors, architectural structures, packaging, and aestheticstructures (e.g., display of images on a piece of jewelry). MEMS devicesof similar structure to those described herein can also be used innon-display applications such as in electronic switching devices.

One interferometric modulator display embodiment comprising aninterferometric MEMS display element is illustrated in FIG. 1. In thesedevices, the pixels are in either a bright or dark state. In the bright(“on” or “open”) state, the display element reflects a large portion ofincident visible light to a user. When in the dark (“off” or “closed”)state, the display element reflects little incident visible light to theuser. Depending on the embodiment, the light reflectance properties ofthe “on” and “off” states may be reversed. MEMS pixels can be configuredto reflect predominantly at selected colors, allowing for a colordisplay in addition to black and white.

FIG. 1 is an isometric view depicting two adjacent pixels in a series ofpixels of a visual display, wherein each pixel comprises a MEMSinterferometric modulator. In some embodiments, an interferometricmodulator display comprises a row/column array of these interferometricmodulators. Each interferometric modulator includes a pair of reflectivelayers positioned at a variable and controllable distance from eachother to form a resonant optical cavity with at least one variabledimension. In one embodiment, one of the reflective layers may be movedbetween two positions. In the first position, referred to herein as thereleased state, the movable layer is positioned at a relatively largedistance from a fixed partially reflective layer. In the secondposition, the movable layer is positioned more closely adjacent to thepartially reflective layer. Incident light that reflects from the twolayers interferes constructively or destructively depending on theposition of the movable reflective layer, producing either an overallreflective or non-reflective state for each pixel.

The depicted portion of the pixel array in FIG. 1 includes two adjacentinterferometric modulators 12 a and 12 b. In the interferometricmodulator 12 a on the left, a movable and highly reflective layer 14 ais illustrated in a released position at a predetermined distance from afixed partially reflective layer 16 a. In the interferometric modulator12 b on the right, the movable highly reflective layer 14 b isillustrated in an actuated position adjacent to the fixed partiallyreflective layer 16 b.

The fixed layers 16 a, 16 b are electrically conductive, partiallytransparent and partially reflective, and may be fabricated, forexample, by depositing one or more layers each of chromium andindium-tin-oxide onto a transparent substrate 20. The layers arepatterned into parallel strips, and may form row electrodes in a displaydevice as described further below. The movable layers 14 a, 14 b may beformed as a series of parallel strips of a deposited metal layer orlayers (orthogonal to the row electrodes 16 a, 16 b) deposited on top ofposts 18 and an intervening sacrificial material deposited between theposts 18. When the sacrificial material is etched away, the deformablemetal layers are separated from the fixed metal layers by a defined airgap 19. A highly conductive and reflective material such as aluminum maybe used for the deformable layers, and these strips may form columnelectrodes in a display device.

With no applied voltage, the cavity 19 remains between the layers 14 a,16 a and the deformable layer is in a mechanically relaxed state asillustrated by the pixel 12 a in FIG. 1. However, when a potentialdifference is applied to a selected row and column, the capacitor formedat the intersection of the row and column electrodes at thecorresponding pixel becomes charged, and electrostatic forces pull theelectrodes together. If the voltage is high enough, the movable layer isdeformed and is forced against the fixed layer (a dielectric materialwhich is not illustrated in this Figure may be deposited on the fixedlayer to prevent shorting and control the separation distance) asillustrated by the pixel 12 b on the right in FIG. 1. The behavior isthe same regardless of the polarity of the applied potential difference.In this way, row/column actuation that can control the reflective vs.non-reflective pixel states is analogous in many ways to that used inconventional LCD and other display technologies.

FIGS. 2 through 5 illustrate one exemplary process and system for usingan array of interferometric modulators in a display application. FIG. 2is a system block diagram illustrating one embodiment of an electronicdevice that may incorporate aspects of the invention. In the exemplaryembodiment, the electronic device includes a processor 21 which may beany general purpose single- or multi-chip microprocessor such as an ARM,Pentium®, Pentium II®, Pentium III®, Pentium IV®, Pentium® Pro, an 8051,a MIPS®, a Power PC®, an ALPHA®, or any special purpose microprocessorsuch as a digital signal processor, microcontroller, or a programmablegate array. As is conventional in the art, the processor 21 may beconfigured to execute one or more software modules. In addition toexecuting an operating system, the processor may be configured toexecute one or more software applications, including a web browser, atelephone application, an email program, or any other softwareapplication.

In one embodiment, the processor 21 is also configured to communicatewith an array controller 22. In one embodiment, the array controller 22includes a row driver circuit 24 and a column driver circuit 26 thatprovide signals to a pixel array 30. The cross section of the arrayillustrated in FIG. 1 is shown by the lines 1-1 in FIG. 2. For MEMSinterferometric modulators, the row/column actuation protocol may takeadvantage of a hysteresis property of these devices illustrated in FIG.3. It may require, for example, a 10 volt potential difference to causea movable layer to deform from the released state to the actuated state.However, when the voltage is reduced from that value, the movable layermaintains its state as the voltage drops back below 10 volts. In theexemplary embodiment of FIG. 3, the movable layer does not releasecompletely until the voltage drops below 2 volts. There is thus a rangeof voltage, about 3 to 7 V in the example illustrated in FIG. 3, wherethere exists a window of applied voltage within which the device isstable in either the released or actuated state. This is referred toherein as the “hysteresis window” or “stability window.” For a displayarray having the hysteresis characteristics of FIG. 3, the row/columnactuation protocol can be designed such that during row strobing, pixelsin the strobed row that are to be actuated are exposed to a voltagedifference of about 10 volts, and pixels that are to be released areexposed to a voltage difference of close to zero volts. After thestrobe, the pixels are exposed to a steady state voltage difference ofabout 5 volts such that they remain in whatever state the row strobe putthem in. After being written, each pixel sees a potential differencewithin the “stability window” of 3-7 volts in this example. This featuremakes the pixel design illustrated in FIG. 1 stable under the sameapplied voltage conditions in either an actuated or releasedpre-existing state. Since each pixel of the interferometric modulator,whether in the actuated or released state, is essentially a capacitorformed by the fixed and moving reflective layers, this stable state canbe held at a voltage within the hysteresis window with almost no powerdissipation. Essentially no current flows into the pixel if the appliedpotential is fixed.

In typical applications, a display frame may be created by asserting theset of column electrodes in accordance with the desired set of actuatedpixels in the first row. A row pulse is then applied to the row 1electrode, actuating the pixels corresponding to the asserted columnlines. The asserted set of column electrodes is then changed tocorrespond to the desired set of actuated pixels in the second row. Apulse is then applied to the row 2 electrode, actuating the appropriatepixels in row 2 in accordance with the asserted column electrodes. Therow 1 pixels are unaffected by the row 2 pulse, and remain in the statethey were set to during the row 1 pulse. This may be repeated for theentire series of rows in a sequential fashion to produce the frame.Generally, the frames are refreshed and/or updated with new display databy continually repeating this process at some desired number of framesper second. A wide variety of protocols for driving row and columnelectrodes of pixel arrays to produce display frames are also well knownand may be used in conjunction with the present invention.

FIGS. 4 and 5 illustrate one possible actuation protocol for creating adisplay frame on the 3×3 array of FIG. 2. FIG. 4 illustrates a possibleset of column and row voltage levels that may be used for pixelsexhibiting the hysteresis curves of FIG. 3. In the FIG. 4 embodiment,actuating a pixel involves setting the appropriate column to −V_(bias),and the appropriate row to +ΔV, which may correspond to −5 volts and +5volts respectively Releasing the pixel is accomplished by setting theappropriate column to +V_(bias), and the appropriate row to the same+ΔV, producing a zero volt potential difference across the pixel. Inthose rows where the row voltage is held at zero volts, the pixels arestable in whatever state they were originally in, regardless of whetherthe column is at +V_(bias), or −V_(bias).

FIG. 5B is a timing diagram showing a series of row and column signalsapplied to the 3×3 array of FIG. 2 which will result in the displayarrangement illustrated in FIG. 5A, where actuated pixels arenon-reflective. Prior to writing the frame illustrated in FIG. 5A, thepixels can be in any state, and in this example, all the rows are at 0volts, and all the columns are at +5 volts. With these applied voltages,all pixels are stable in their existing actuated or released states.

In the FIG. 5A frame, pixels (1,1), (1,2), (2,2), (3,2) and (3,3) areactuated. To accomplish this, during a “line time” for row 1, columns 1and 2 are set to −5 volts, and column 3 is set to +5 volts. This doesnot change the state of any pixels, because all the pixels remain in the3-7 volt stability window. Row 1 is then strobed with a pulse that goesfrom 0, up to 5 volts, and back to zero. This actuates the (1,1) and(1,2) pixels and releases the (1,3) pixel. No other pixels in the arrayare affected. To set row 2 as desired, column 2 is set to −5 volts, andcolumns 1 and 3 are set to +5 volts. The same strobe applied to row 2will then actuate pixel (2,2) and release pixels (2,1) and (2,3). Again,no other pixels of the array are affected. Row 3 is similarly set bysetting columns 2 and 3 to −5 volts, and column 1 to +5 volts. The row 3strobe sets the row 3 pixels as shown in FIG. 5A. After writing theframe, the row potentials are zero, and the column potentials can remainat either +5 or −5 volts, and the display is then stable in thearrangement of FIG. 5A. It will be appreciated that the same procedurecan be employed for arrays of dozens or hundreds of rows and columns. Itwill also be appreciated that the timing, sequence, and levels ofvoltages used to perform row and column actuation can be varied widelywithin the general principles outlined above, and the above example isexemplary only, and any actuation voltage method can be used with thepresent invention.

The details of the structure of interferometric modulators that operatein accordance with the principles set forth above may vary widely. Forexample, FIGS. 6A-6C illustrate three different embodiments of themoving mirror structure. FIG. 6A is a cross section of the embodiment ofFIG. 1, where a strip of metal material 14 is deposited on orthogonallyextending supports 18. In FIG. 6B, the moveable reflective material 14is attached to supports at the corners only, on tethers 32. In FIG. 6C,the moveable reflective material 14 is suspended from a deformable layer34. This embodiment has benefits because the structural design andmaterials used for the reflective material 14 can be optimized withrespect to the optical properties, and the structural design andmaterials used for the deformable layer 34 can be optimized with respectto desired mechanical properties. The production of various types ofinterferometric devices is described in a variety of publisheddocuments, including, for example, U.S. Published Application2004/0051929. A wide variety of well known techniques may be used toproduce the above described structures involving a series of materialdeposition, patterning, and etching steps.

FIG. 7 illustrates a package structure 800 in which an interferometricmodulator 830 is packaged on a transparent substrate 810 without aconventional backplane or cap. The package structure 800 illustrated inFIG. 7 may eliminate the need for not only a backplane but also aseparate seal as well as a desiccant.

In accordance with the embodiment shown in FIG. 7, instead of sealing abackplane to the transparent substrate to encapsulate theinterferometric modulator 830, as discussed above, a thin film orsuperstructure 820 is deposited over the transparent substrate 810 toencapsulate the interferometric modulator 830 within the packagestructure 800. The thin film 820 protects the interferometric modulator830 from harmful elements in the environment.

A method of packaging an interferometric modulator according to theembodiment shown in FIG. 7 will be discussed in more detail below. Thepackages and packaging methods described herein may be used forpackaging any interferometric modulator, including, but not limited to,the interferometric modulators described above.

As discussed above, the interferometric modulator 830 is configured toreflect light through the transparent substrate and includes movingparts, such as the movable mirrors 14 a, 14 b. Therefore, to allow suchmoving parts to move, a gap or cavity 840 is preferably created betweensuch moving parts and the thin film 820. The gap or cavity 840 allowsthe mechanical parts, such as the movable mirrors 14 a, 14 b, of theinterferometric modulator 830 to move. It will be understood that beforethe thin film 820 can be deposited to encapsulate the interferometricmodulator 830, a sacrificial layer 850 (shown in FIG. 9) is preferablydeposited over the interferometric modulator 830 and the transparentsubstrate 810, and then removed, to create a cavity 840 between theinterferometric modulator 830 and the thin film 820. This will bedescribed in more detail below.

FIG. 8 shows one embodiment of a method of packaging an interferometricmodulator without a conventional backplane or cap. A transparentsubstrate 810 is first provided at Step 900 and the interferometricmodulator 830 is formed on the transparent substrate 810 at Step 910.The interferometric modulator 830 is preferably formed in accordancewith the processes described with reference to FIGS. 1-6. Thetransparent substrate 810 may be any transparent substance capable ofhaving thin film, MEMS devices built upon it. Such transparentsubstances include, but are not limited to, glass, plastic, andtransparent polymers. Images are displayed through the transparentsubstrate 810, which serves as an imaging surface.

After the interferometric modulator 830 has been formed on thetransparent substrate 810, a sacrificial layer 850 is preferablydeposited over the upper surfaces of the interferometric modulator 830and the transparent substrate 810 in Step 920. The sacrificial layer 850is then patterned in Step 930, using photolithographic techniques. Thispatterning process preferably localizes the sacrificial layer 850 to theinterferometric modulator 830, exposing the transparent substrate 810around the periphery of the interferometric modulator 830. After thesacrificial layer 850 has been deposited and patterned, a thin film 820is then deposited over the entire structure, in Step 940. The thin film820 is then patterned in Step 950, using photolithographic techniques.This patterning process localizes the thin film 820 to the sacrificiallayer 850. This patterning step also provides features in the thin film820 that enable the subsequent removal of the sacrificial layer 850. Itshould be noted that, at this point in the process, additionalsacrificial layers may or may not remain within the interferometricmodulator structure. The patterning step 930 allows for removal ofsacrificial layer 850 as well as for removal of any sacrificial layersremaining within the interferometric modulator 830. In Step 960, thesacrificial layer 850 and any sacrificial layers within theinterferometric modulator 830 are removed, leaving a cavity 840 betweenthe interferometric modulator 830 and the thin film 820, completingprocessing of the interferometric modulator 830. In Step 970, thefeatures or openings in the thin film 820 are sealed.

In accordance with an embodiment, an interferometric modulator 830 ispreferably formed on a transparent substrate 810. It will be understoodthat the fixed mirrors 16 a, 16 b of the interferometric modulator 830are adjacent the transparent substrate 810 and the movable mirrors 14 a,14 b are formed over the fixed mirrors 16 a, 16 b such that the movablemirrors 14 a, 14 b may move within the cavity 840 of the packagestructure of the embodiment shown in FIG. 7.

To form the interferometric modulator 830, the transparent substrate 810in one embodiment is covered with indium tin oxide (ITO). The ITO may bedeposited by standard deposition techniques, including chemical vapordeposition (CVD) and sputtering, preferably to a thickness of about 500Å. A relatively thin layer of chrome is preferably deposited over theITO. The ITO/chrome bilayer is then etched and patterned into columns toform the column electrodes 16 a, 16 b. A layer of silicon dioxide (SiO₂)is preferably formed over the ITO/chrome columns to create partiallyreflective fixed mirrors 16 a, 16 b. A sacrificial layer of silicon (Si)is preferably deposited (and later released) over the structure tocreate a resonant optical cavity between the fixed mirrors 16 a, 16 band the movable mirrors 14 a, 14 b. In other embodiments, thissacrificial layer may be formed of molybdenum (Mo), tungsten (W), ortitanium (Ti).

Another mirror layer, preferably formed of aluminum, is deposited overthe sacrificial layer of silicon to form the movable mirrors 14 a, 14 bof the interferometric modulator 830. This mirror layer is deposited andpatterned into rows orthogonal to the column electrodes 16 a, 16 b tocreate the row/column array described above. In other embodiments, thismirror layer may comprise highly reflective metals, such as, forexample, silver (Ag) or gold (Au). Alternatively, this mirror layer maybe a stack of metals configured to give the proper optical andmechanical properties.

The sacrificial layer of silicon is removed, preferably using a gasetching process, after the movable mirrors 14 a, 14 b are formed tocreate the optical cavity between the fixed mirrors 16 a, 16 b and themovable mirrors 14 a, 14 b. In an embodiment, this sacrificial layer isetched away after the thin film 820 is formed. Standard etchingtechniques may be used to remove the sacrificial layer of silicon. Theparticular release etching will depend on the material to be released.For example, xenon diflouride (XeF₂) may be used to remove the siliconsacrificial layer. In one embodiment, the sacrificial layer of siliconbetween the mirrors 16 a, 16 b, 14 a, 14 b is removed after the thinfilm 820 is formed. The skilled artisan will appreciate that each layerof the interferometric modulator 830 is preferably deposited andpatterned using standard deposition techniques and standardphotolithographic techniques.

As shown in FIG. 9, after the interferometric modulator 830 is formed onthe transparent substrate 810, another sacrificial layer 850 isdeposited over the upper surfaces of the interferometric modulator 830and the transparent substrate 810. The sacrificial layer 850 may beformed of a material, such as, for example, molybdenum (Mo), silicon(Si), tungsten (W), or titanium (Ti), which is capable of being releasedafter deposition of the thin film 820. In an embodiment, the sacrificiallayer 850 is formed of a material, such as a polymer, spin-on glass, oroxide. The removal processes, which may differ depending on the materialof the sacrificial layer, will be described in more detail below.

The skilled artisan will appreciate that the upper sacrificial layer 850may be formed of any of molybdenum (Mo), silicon (Si), tungsten (W),titanium (Ti), polymer, spin-on glass, or oxide so long as the materialprovides sufficient step coverage and can be deposited to the desiredthickness. The thickness of the sacrificial layer 850 should besufficient to separate the thin film 820 and the interferometricmodulator 830. In one embodiment, the upper sacrificial layer 850 isdeposited to a thickness in the range of about 1000 Å to 1 μm, and morepreferably in a range of about 1000 Å to 5000 Å. In one embodiment, thesacrificial layer 850 is patterned and etched using standardphotolithographic techniques.

In one embodiment, the thin film 820 can be deposited over the entireupper surface of the sacrificial layer 850, as shown in FIG. 10. Thethin film 820 may be formed over the sacrificial layer 850 using knowndeposition techniques. After the thin film 820 is patterned and etched,the sacrificial layer 850 is released to form a cavity 840 in which themovable mirrors 14 a, 14 b may move, as shown in FIG. 8.

The thin film 820 is preferably patterned and etched to form at leastone opening therein through which a release material, such as xenondiflouride (XeF₂), may be introduced into the interior of the packagestructure 800 to release the sacrificial layer 850. The number and sizeof these openings depend on the desired rate of release of thesacrificial layer 850. The openings may be positioned anywhere in thethin film 820. In certain embodiments, the sacrificial layer 850 and thesacrificial layer within the interferometric modulator (between thefixed mirrors 16 a, 16 b and the movable mirrors 14 a, 14 b) may bereleased at the same time. In other embodiments, the sacrificial layer850 and the sacrificial layer within the interferometric modulator arenot removed at the same time, with the sacrificial layer 850 beingremoved prior to the removal of the sacrificial layer within theinterferometric modulator.

An alternative release technique is shown by the embodiment in FIG. 11.FIG. 11 is a top view of an embodiment of the package structure 800after the thin film 820 has been deposited and patterned and before thesacrificial layer 850 is released. As shown in FIG. 11, the sacrificiallayer 850 is deposited and patterned such that it has a plurality ofprotrusions 855. The thin film 820 is then deposited over thesacrificial layer 850 and the transparent substrate 810. After the thinfilm 820 is deposited, it is then preferably etched back on each side,as shown in FIG. 11. The package structure 800 can then be exposed tothe release material, such as xenon diflouride (XeF₂), which reactsfirst with the exposed sacrificial layer 850 material and then entersthe package structure 800 through the openings created at theprotrusions 855 by the removal of the sacrificial layer 850 on the sidesof the package structure. It will be understood that the number and sizeof the protrusions 855 will depend on the desired rate of release of thesacrificial layer 850.

To remove a sacrificial layer of molybdenum (Mo), silicon (Si), tungsten(W), or titanium (Ti), xenon diflouride (XeF₂) may be introduced intothe interior of the package structure 800 through an opening or openingsin the thin film 820. Such openings in the thin film 820 are preferablycreated by etching an opening in the thin film 820. The xenon diflouride(XeF₂) reacts with the sacrificial layer 850 to remove it, leaving acavity 840 between the interferometric modulator 830 and the thin film820. A sacrificial layer 850 formed of spin-on glass or oxide ispreferably gas etched or vapor phase etched to remove the sacrificiallayer 850 after the thin film 820 has been deposited. The skilledartisan will appreciate that the removal process will depend on thematerial of the sacrificial layer 850.

The skilled artisan will also appreciate that the cavity 840 isnecessary behind the interferometric modulator 830 to allow themechanical parts, such as the movable mirrors 14 a, 14 b, of theinterferometric modulator 830 to be free to move. The resulting height hof the cavity 840 depends on the thickness of the sacrificial layer 850.

In some embodiments, the thin film 820 may be any type of material thatis hermetic or hydrophobic, including, but not limited to, nickel,aluminum, and other types of metals and foils. The thin film 820 mayalso be formed of an insulator, including, but not limited to, silicondioxide, aluminum oxide, or nitrides.

Alternatively, the thin film 820 may be formed of a non-hermeticmaterial. Suitable non-hermetic materials include polymers, such as, forexample, PMMA, epoxies, and organic or inorganic spin-on glass (SOG)type materials. If non-hermetic materials are used for the thin film820, an overcoat layer 860, as shown in FIG. 12, is preferably formedover the non-hermetic thin film to provide additional protection to theinterferometric modulator 830 after the sacrificial layer 850 isremoved, as shown in FIG. 12. Such an overcoat layer 860 is preferablyformed of a vapor barrier and has a thickness of about 1000 Å to about10,000 Å. In one embodiment, the overcoat layer 860 is Barix™, a thinfilm coating commercially available from Vitex Systems, Inc. in SanJose, Calif. Such an overcoat may be multi-layered in which some layersmay serve gas hermeticity purposes, and some layers, as described below,may serve mechanical purposes.

In certain embodiments in which the thin film 820 is a hydrophobicmaterial, it does not necessarily create a hermetic seal, but maynevertheless eliminate the need for a conventional backplane. It will beappreciated that any further moisture barrier required can beincorporated in the next step of packaging at the module level.

The thin film 820 can be deposited by chemical vapor deposition (CVD) orother suitable deposition methods to a thickness of about 1 μm. Theskilled artisan will understand that the thickness of the thin film 820may depend on the particular material properties of the materialselected for the thin film 820.

The thin film 820 may be either transparent or opaque. Because imagesare not displayed through the thin film 820, but rather through thetransparent substrate 810, it is understood that the thin film 820 neednot be transparent. The skilled artisan will appreciate that transparentmaterials, such as spin-on glass, may be used to form the thin film 820as they may have material properties that are suitable for use as a thinfilm 820 for protection of the interferometric modulator 830. Forexample, a material such as spin-on glass, which is transparent, mayprovide more strength and protection to the interferometric modulator830 within the package structure 800.

After the sacrificial layer 850 is released, the opening(s) in the thinfilm 820 are preferably sealed. In an embodiment, epoxy is used to sealthese openings. The skilled artisan will appreciate that other materialsmay be used as well and that materials having high viscosity arepreferred. If the openings are sufficiently small (e.g. less than 1μ),another layer of the thin film 820 material may be used to seal theopenings.

In some embodiments, including, but not limited to, certain embodimentshaving a hermetic thin film 820, an overcoat layer 860 may be depositedover the thin film 820 after the sacrificial layer 850 has been removed,as shown in FIG. 12. The overcoat layer is preferably formed of apolymer and preferably has a thickness of about 1 μm to severalmillimeters. The overcoat layer 860 provides additional strength andstiffness to the thin film 820. In certain embodiments where theopening(s) in the thin film 820 are sufficiently small (e.g. less than1μ), the overcoat layer 860 may be used to seal the openings rather thananother layer of the thin film 820, as described above.

The thin film 820 preferably hermetically seals the interior the packagestructure 800 from the ambient environment, as shown in FIG. 7. As thethin film 820 may provide a hermetic seal, the need for a desiccant istherefore eliminated as the hermetic seal prevents moisture fromentering the package structure 800 from the ambient environment. Inanother embodiment, the thin film 820 provides a semi-hermetic seal anda desiccant is included within the package structure 800 to absorbexcess moisture.

A desiccant may be used to control moisture resident within the packagestructure 800. However, as the thin film 820 may provide a hermeticseal, depending on the material selected, a desiccant is not necessaryto prevent moisture from traveling from the atmosphere into the interiorof the package structure 800. In the case of a semi-hermetic thin film820, the amount of desiccant required is reduced.

In an embodiment, the method of packaging an interferometric modulatoraccording to this embodiment integrates the sealing of the packagestructure 800 into the front-end processing and eliminates the need fora separate backplane, desiccant, and seal, thereby lowering the cost ofpackaging. In another embodiment, the thin film 820 reduces the amountof desiccant required rather than eliminating the need for a desiccant.Packaging in accordance with these embodiments reduces the materialconstraints with respect to both the desiccant and seal, therebyallowing a greater choice or materials, geometries, and opportunities toreduce costs. The thin film 820 can reduce hermetic requirements toallow for not only elimination of a backplane but also allows anyadditional moisture barrier requirements to be incorporated into themodule level packaging. It is generally desirable to keep the packagestructure as thin as possible and the package structure 800 shown inFIG. 7 provides for a thin structure.

The elimination of the need for a desiccant also allows the packagestructure 800 to be even thinner. Typically, in packages containingdesiccants, the lifetime expectation of the device may depend on thelifetime of the desiccant. When the desiccant is fully consumed, theinterferometric modulator display will fail as sufficient moistureenters the package structure to cause damage to the interferometricmodulator. The theoretical maximum lifetime of the device is determinedby the water vapor flux into the package as well as the amount and typeof desiccant. In this package structure 800, the interferometricmodulator 830 will not fail due to a consumed desiccant as the packagestructure 800 of this embodiment does not contain any desiccant.

In another embodiment, the thin film 820 is not hermetic and may bepermeable to xenon diflouride (XeF₂) or another removal gas, whichreacts with the sacrificial layer 850 to remove it, leaving a cavity 840between the interferometric modulator 830 and the thin film 820.According to this embodiment, some suitable materials for the thin film820 include, but are not limited to porous alumina and certain aerogels.In this embodiment, it is not necessary for the thin film 820 to beformed with any openings so long as it is permeable to xenon diflouride(XeF₂) or another removal gas. Preferably, after removal of thesacrificial layer 850, a hermetic overcoat layer 860 is deposited overthe thin film 820 to hermetically seal the package structure 800. Inthese embodiments, the overcoat layer 860 is preferably formed of ametal.

While the above detailed description has shown, described, and pointedout novel features of the invention as applied to various embodiments,it will be understood that various omissions, substitutions, and changesin the form and details of the device or process illustrated may be madeby those skilled in the art without departing from the spirit of theinvention. As will be recognized, the present invention may be embodiedwithin a form that does not provide all of the features and benefits setforth herein, as some features may be used or practiced separately fromothers.

1. A method of manufacturing a display, the method comprising: providingan electro-mechanical device, wherein said electro-mechanical devicecomprises a first sacrificial layer; depositing a second sacrificiallayer over said electro-mechanical device, wherein said secondsacrificial layer is exposed to a portion of said first sacrificiallayer; depositing a thin film backplane over and in contact with saidsecond sacrificial layer, wherein the thin film backplane has anopening; and after depositing the thin film backplane, removing saidfirst and said second sacrificial layers, wherein at least a part ofsaid first sacrificial layer is removed concurrently with at least apart of said second sacrificial layer, wherein removing said secondsacrificial layer provides a gap above said electro-mechanical deviceand below said thin film backplane.
 2. The method of claim 1, whereinsaid electro-mechanical device comprises an interferometric modulator.3. The method of claim 2, wherein said first sacrificial layer isdisposed in an optical cavity of said interferometric modulator.
 4. Themethod of claim 1, wherein said electro-mechanical device comprises anarray of moveable mirrors configured to interferometrically modulatelight.
 5. The method of claim 1, wherein all of said first and all ofsaid second sacrificial layers are removed at the same time.
 6. Themethod of claim 1, wherein said thin film backplane comprises a hermeticmaterial.
 7. The method of claim 1, wherein said first sacrificial layeror said second sacrificial layer is formed of molybdenum, silicon,tungsten, or titanium.
 8. The method of claim 1, wherein said firstsacrificial layer or said second sacrificial layer is removed with xenondiflouride.
 9. The method of claim 1 further comprising depositing anovercoat layer over said thin film backplane.
 10. The method of claim 1,wherein said electro-mechanical device comprises amicroelectromechanical systems device.
 11. A method of manufacturing adisplay comprising a plurality of electro-mechanical devices, the methodcomprising: providing an electro-mechanical device, wherein saidelectro-mechanical device comprises: a first sacrificial layer; and afirst opening into said electro-mechanical device exposing saidsacrificial layer; providing a thin film backplane over saidelectro-mechanical device, wherein the thin film backplane comprises asecond opening; providing a second sacrificial layer between said thinfilm backplane and said electro-mechanical device; introducing a releasematerial through said first and second openings to release the firstsacrificial layer and second sacrificial layer, and wherein at least apart of said first sacrificial layer is removed concurrently with atleast a part of said second sacrificial layer.
 12. The method of claim11, wherein all of said first sacrificial layer and all of said secondsacrificial layer are removed at the same time.
 13. The method of claim11, wherein said release material is xenon diflouride.
 14. The method ofclaim 11, wherein said electro-mechanical device comprises aninterferometric modulator.
 15. The method of claim 11, wherein saidelectro-mechanical device comprises an array of moveable mirrorsconfigured to interferometrically modulate light.
 16. The method ofclaim 11, wherein said electro-mechanical device comprises amicroelectromechanical systems device.
 17. A display device, comprising:a transparent substrate; an interferometric modulator disposed on thetransparent substrate, said interferometric modulator comprising: afirst sacrificial layer; and a first opening exposing said firstsacrificial layer; and a thin film backplane sealing saidinterferometric modulator within a package between said transparentsubstrate and said thin film backplane, wherein a second sacrificiallayer is positioned between said thin film backplane and saidinterferometric modulator and contacts said first sacrificial layerexposed at said first opening, and wherein a second opening exists insaid thin film backplane.
 18. The method of claim 1, wherein said secondsacrificial layer is deposited to a thickness in the range of about 1000Å to about 5000 Å.
 19. The method of claim 1, wherein said thin film isabout 1 μm thick.
 20. The method of claim 2, wherein saidinterferometric modulator comprises a layer of indium tin oxide of about500 Å thick.